1. Field of the Invention
This invention relates to a method of making an immersion nozzle and a long stopper used for the continuous casting of steel, and more specifically, to a method of making an immersion nozzle and a long stopper consisting mainly of natural flake graphite and zircon which provides especially good results when used for the continuous casting of high manganese steel.
2. Description of the Prior Art
An immersion nozzle is used for pouring molten steel into a mold from a receptacle such as a tundish. In use, the lower end of the nozzle is immersed in the molten steel within the mold to shield the molten steel from the air, to maintain the temperature of the flowing molten steel, and to prevent oxidation, disorder of the molten steel or the inclusion of a powdery coating agent sprayed onto the upper surface of the molten steel within the mold. Thus, it is an important device which is very effective to improve the quality of the cast product. Since it is used under very severe conditions and is very susceptible to corrosion or spalling due to the high temperature molten steel flow or slag, various refractory materials have previously been proposed for use as a material for immersion nozzles, for example, high silica-content immersion nozzles, and, more recently, fused silica, graphite-alumina, or zircon immersion nozzles.
A long stopper is provided inside the tundish, and serves to control the flow rate of the molten steel from the tundish over long periods of time. Hence, it requires the same properties as the immersion nozzle.
The prior art high silica immersion nozzzles have the defect that they are susceptible to corrosion by the molten steel, and the nozzle diameter increases during use. The fused silica immersion nozzles of the prior art have the advantage of superior resistance to spalling and to corrosion by the powdery coating agent. However, they are susceptible to corrosion by molten steel having a high manganese content, and when used for aluminum-killed steel, alumina deposits on the inside surface of the nozzle and tends to cause blockage of the nozzle. The graphite-alumina immersion nozzles of the prior art have high resistance to corrosion by molten steel, but undergo heavy corrosion due to the powdery coating agent and slag. The zircon-immersion nozzles of the prior art have high resistance to corrosion by the powdery coating agent and slag, but do not possess resistance to spalling. Moreover, when such a zircon immersion nozzle is used for aluminum-killed steel, it has the defect of clogging due to the deposition of alumina. Thus, none of the conventional immersion nozzles have proven entirely satisfactory.